everytime i open up photoshop it opens up like 20 other previous images that i had opened in the app
This is a feature in OS X called "Resume". Apps carry on from where they left off, even after quitting.
You can turn it off, as outlines above, or you can quit and close all windows by using <command><alt> Q
Much has been written about the radical changes from traditional Desktop metaphors in OS X 10.7 and above. You may have noticed some other features too, like Auto-Save and Versions.
You may want to take some time to read about all the features and functions of your OS.
Here's a good (lengthy) starting point:
http://arstechnica.com/apple/2012/07/os-x-10-8/